46 research outputs found
Exclusive diffractive processes and the quark substructure of mesons
Exclusive diffractive processes on the nucleon are investigated within a
model in which the quark-nucleon interaction is mediated by Pomeron exchange
and the quark substructure of mesons is described within a framework based on
the Dyson-Schwinger equations of QCD. The model quark-nucleon interaction has
four parameters which are completely determined by high-energy and elastic scattering data. The model is then used to predict vector-meson
electroproduction observables. The obtained - and -meson
electroproduction cross sections are in excellent agreement with experimental
data. The predicted dependence of -meson electroproduction also
agrees with experimental data. It is shown that confined-quark dynamics play a
central role in determining the behavior of the diffractive, vector-meson
electroproduction cross section. In particular, the onset of the asymptotic
behavior of the cross section is determined by a momentum scale that is
set by the current-quark masses of the quark and antiquark inside the vector
meson. This is the origin of the striking differences between the
dependence of -, - and -meson electroproduction cross
sections observed in recent experiments.Comment: 53 pages, 23 figures, revtex and epsfig. Minor additions to tex
The dependence of the hard diffractive photoproduction of vector meson or photon and the range of pQCD validity
We consider two coupled problems.
We study the dependence on photon virtuality for the semihard
quasi--elastic photoproduction of neutral vector mesons on a quark, gluon or
real photon (at
GeV)). To this end we calculate the corresponding amplitudes (in an
analytical form) in the lowest nontrivial approximation of perturbative QCD. It
is shown that the amplitude for the production of light meson varies very
rapidly with the photon virtuality near .
We estimate the bound of the pQCD validity region for such processes. For the
real incident photon the obtained bound for the meson production is very
high. This bound decreases fast with the increase of , and we expect that
the virtual photoproduction at HERA gives opportunity to test the pQCD results.
The signature of this region is discussed. For the hard Compton effect the pQCD
should work good at not too high , and this effect seems measurable
at HERA.Comment: ReVTeX, 36 pages, 5 Postscript figures, uses epsf.st
The Wave Function of 2S Radially Excited Vector Mesons from Data for Diffraction Slope
In the color dipole gBFKL dynamics we predict a strikingly different Q^2 and
energy dependence of the diffraction slope for the elastic production of ground
state V(1S) and radially excited V'(2S) light vector mesons. The color dipole
model predictions for the diffraction slope for \rho^0 and \phi^0 production
are in a good agreement with the data from the fixed target and collider HERA
experiments. We present how a different form of anomalous energy and Q^2
dependence of the diffraction slope for V'(2S) production leads to a different
position of the node in radial wave function and discuss a possibility how to
determine this position from the fixed target and HERA data.Comment: 20 pages and 6 figures. Title change
A Unified Model of Exclusive , and \jpsi Electroproduction
A two-component model is developed for diffractive electroproduction of
, and \jpsi, based on non-perturbative and perturbative
two-gluon exchange. This provides a common kinematical structure for
non-perturbative and perturbative effects, and allows the role of the
vector-meson vertex functions to be explored independently of the production
dynamics. A good global description of the vector-meson data is obtained.Comment: 30 pages, 35 figure
asymmetry and semi-inclusive production of pions in DIS
We investigate unambiguities in the extraction of the
asymmetry from semi-inclusive production of pions in DIS. The role of several
effects beyond the quark-parton model (QPM) which lead to and and may therefore cloud such an
extraction is studied. The results are discussed in the context of the recent
HERMES data. We find that the interaction of the resolved photon with the
nucleon significantly modifies the observed asymmetry. The
exclusive elastic production of mesons plays a similar role for the
large- data sample. Our estimate shows a rather small effect of the
spectator mechanism. Nuclear effects in the deuteron also look potentially
important but are difficult to estimate quantitatively.
Throughout the paper we make in addition several general remarks concerning
semi-inclusive and exclusive production of mesons.Comment: 47 pages, LaTeX with 19 eps figure
Proceedings of the Sixth International Workshop on Web Caching and Content Distribution
OVERVIEW
The International Web Content Caching and Distribution Workshop (WCW) is a premiere technical meeting for researchers and practitioners interested in all aspects of content caching, distribution and delivery on the Internet. The 2001 WCW meeting was held on the Boston University Campus. Building on the successes of the five previous WCW meetings, WCW01 featured a strong technical program and record participation from leading researchers and practitioners in the field. This report includes all the technical papers presented at WCW'01.
Note: Proceedings of WCW'01 are published by Elsevier. Hardcopies of these proceedings can be purchased through the workshop organizers. As a service to the community, electronic copies of all WCW'01 papers are accessible through Technical Report BUCS‐TR‐2001‐017, available from the Boston University Computer Science Technical Report Archives at http://www.cs.bu.edu/techreps. [Ed.note: URL outdated. Use http://www.bu.edu/cs/research/technical-reports/ or http://hdl.handle.net/2144/1455 in this repository to access the reports.]Cisco Systems; InfoLibria; Measurement Factory Inc; Voler
Exclusive meson electroproduction from hydrogen at CLAS
The longitudinal and transverse components of the cross section for the reaction were measured in Hall B at Jefferson
Laboratory using the CLAS detector. The data were taken with a 4.247 GeV
electron beam and were analyzed in a range of from 0.2 to 0.6 and of
from 1.5 to 3.0 GeV. The data are compared to a Regge model based on
effective hadronic degrees of freedom and to a calculation based on Generalized
Parton Distributions. It is found that the transverse part of the cross section
is well described by the former approach while the longitudinal part can be
reproduced by the latter.Comment: 6 pages, 4 figure